Wednesday, April 1, 2009

A common tenet in user interface design is to be consistent, especially to be consistent with de facto standards. It's certainly a good goal, but I think that kind of consistency can be pushed too far. I recently thought of some real world examples: humble, ordinary, every day doors.

Doors share a common functional requirement: be closed sometimes and be open others. That leaves a lot of room for design though, like what color should it be? Or, more importantly, which way should it open?

The De Facto Standard

Doors in offices, bedrooms, bathrooms, etc. tend to open inwards. Why? Because a bathroom door opening outwards could suddenly thrust a large solid object into a public walkway. Black eyes, broken noses, and other hilarity ensue.

The Exception

There's a major exception to this rule. Public places where there are likely to be crowds like stores tend to have doors that open outwards. Why? Because a dangerous fire is far more likely to occur inside than outside, and if one did occur then a rushing crowd could jam an inward opening door closed. Panic, trampling, and other hilarity ensue.

The Exception to the Exception

There's a major exception to the exception to the rule. An airliner is certainly a crowded public place where you would want to quickly get people out in an emergency. Yet the door opens inwards. Why? Because at altitude the airplane will be pressurized. The inside pressure will be significantly higher than the outside and must be contained. The doorway is a significant weakening in that containment, but a door that opens inwards works just like a drain plug. The pressure difference keeps it firmly sealed and in place. A door that opened outward would be very likely to, um, open outward. Ejected flight attendants, hypoxia, and other hilarity ensue.

The Take Away

De facto standards are good and often have good reason to exist. But they don't always apply. Exceptions and exceptions to exceptions sometimes make more sense. Following a standard is no substitute for doing actual design.

10 comments:

Nice but I think you're using the wrong example. Doors have different ways of opening, true. But first of all look at the amount of trouble this is causing. How many times have you seen people trying to push when they have to pull? And that happens even when there's a sign clearly stating that you have to pull. That just sounds like bad design, but obviously we haven't really been able to come up with a better answer yet.

The better example of standards would be the door handles.

The ones that turn cause the same amount of problems as the push vs pull. Luckily there aren't many of them.

The standard ones that you have to push down seem to cause the least amount of trouble.

But I've lived in a house where the previous owners had smart cats that would jump up and open the doors so they reinstalled the handles up-side-down. The problem was it worked just as well for people as for cats! You had to explain it to each new person that came to visit because nobody would figure it out on their own, it was just too strange!

Well, this was just a nice anecdote, I agree completely with the last line of your article of course.

"How many times have you seen people trying to push when they have to pull? And that happens even when there's a sign clearly stating that you have to pull. That just sounds like bad design, but obviously we haven't really been able to come up with a better answer yet."

Actually, there is a design that seem to cause less confusion but it's not used as much as I would like. A lot of doors have two different types of handles:

1) a flat surface on the side where you push2) a grip friendly handle on the side where you pull

There are even handles with an opening mechanism that is activated either by pushing or pulling.

I kind of liked the example partly because of our apparent problems of making something so simple as doors easy and intuitive to use.

I agree that when you have to put an explaining text (such as pull on a door) it's a hint that there is room for improvement in the design.

Flat surface for pushing are hardly ideal: they make it very easy to push with a lot of energy..

Ensuring that whoever is on the other side of the door is going to be very annoyed!

So IMHO in both case, there should be handles, perhaps a standardisation of two different designs for pushing and pulling would solve the issue.Or a transparent surface on the door so you see if someone is on the other side :) Not ideal for WC-doors but works very well on "public doors" such as entrances to buildings etc.

Depends on what you mean by "open." Pressurized aircraft always use a kind of "plug door." http://en.wikipedia.org/wiki/Plug_door Like a drain plug, it is held in place by a pressure difference - the higher pressure inside the airplane pushes the door into a slot from the inside. When the pressure difference is gone the door can be pulled inwards to unseal it.

However, there's not much space inside the airplane so it's very common for the door to be shaped so that after unsealing the door can be twisted slightly and pushed out through the opening.

Closing the door is a reverse of the process. The door is pulled through the opening, lined up, and pushed firmly in place from the inside.